The proposed research is a cell biological analysis of some of the processes involved in neuronal development. The main goal is to develop an understanding: (1) of the mechanism of plasmalemmal expansion in the growing neurite, (2) of the process of maturation and regional differentiation of the plasma membrane, and (3) of the role of growth cone plasmalemma in the mechanisms of guidance and recognition in nervous system development. Nerve tissue cultures are used for binding studies with ferritin-conjugated lectins for electron microscopic analysis of cell surface carbohydrates. Parameters to be studied include: (a) lectin binding as a function of maturation and type of neurite, and (b) appearance of new lectin receptors, and their relative movement, during nerve fiber growth. Complementary studies attempt to analyze (c), by pulse-chase experiments and electron microscope radioautography, the transport of membrane precursors to their sites of plasmalemmal insertion, and to investigate (d), by freeze-fracture, the density of intramembranous particles as a function of time and maturation in various areas of neuronal plasmalemma.